Auxiliary Electrode Projections for OLED Luminance Uniformity
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Solution Overview
Problem
In large-area lighting and display devices, voltage drops across electrodes lead to luminance unevenness due to high resistance, and existing methods for providing auxiliary electrodes to mitigate this issue often damage the electroluminescent (EL) layer or result in reduced light extraction efficiency.
Innovation Solution
Forming an auxiliary electrode with projections and depressions before the EL layer, ensuring electrical connection to the upper electrode while maintaining insulation to prevent light emission from non-transmissive regions, thereby reducing voltage drops and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an auxiliary electrode is formed after the EL layer using photolithography, then conductivity is improved, but the EL layer is damaged by developer and remover
Solution Approach 1:
The auxiliary electrode is formed before the EL layer is deposited, rather than after. This preliminary action allows the electrode structure to be in place before the sensitive EL layer is introduced, avoiding subsequent damage from photolithography chemicals. The sequence is reversed: substrate → auxiliary electrode → EL layer → upper electrode.
Solution Approach 2:
The electrode system is segmented into three parts: the original lower electrode, the auxiliary electrode formed with projections and depressions, and the upper electrode. This segmentation allows the auxiliary electrode to provide conductivity enhancement while the projections and depressions create insulation regions that prevent short-circuiting and protect the EL layer.
2Reliability
If an auxiliary electrode is formed using metal mask, then conductivity is improved, but the EL layer is damaged by mask pressure and foreign particles
Solution Approach 1:
The auxiliary electrode is formed before the EL layer deposition, eliminating the need for subsequent metal mask operations that would press against and potentially damage the already-formed EL layer. The mask-related damage risks are avoided by completing the auxiliary electrode formation in earlier processing steps.
3Reliability
If auxiliary electrode is provided to suppress voltage drop, then luminance unevenness is reduced, but light extraction efficiency decreases due to opaque auxiliary electrode
Solution Approach 1:
The auxiliary electrode is given a non-uniform surface morphology with projections and depressions. The projections create localized regions where the EL layer is thinner or disconnected, providing electrical connection paths while the depressions allow light to pass through to the upper electrode. This local variation in structure allows simultaneous achievement of conductivity enhancement and light transmission.
Solution Approach 2:
The auxiliary electrode structure is extended into the vertical dimension with projections rising from the substrate plane. This three-dimensional structure allows the electrode to provide conductivity in the lateral direction while the vertical projections create gaps that permit light extraction in the vertical direction, resolving the contradiction between electrical and optical functions.
4Illumination intensity
If transparent electrode with high resistivity is used, then light transmission is maintained, but voltage drop occurs in large-area substrates
Solution Approach 1:
The functions of light transmission and low resistance are merged into a single auxiliary electrode structure. By forming the auxiliary electrode with projections and depressions before EL layer deposition, the structure achieves both electrical conductivity (through the continuous electrode material) and optical transparency (through the gaps created by projections and depressions).
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces damage to the EL layer, suppresses luminance unevenness, and improves light extraction efficiency by allowing for a top-emission structure with a wider material selection for the substrate, including high thermal conductivity materials.
Implementation Method 1
an auxiliary electrode having a projection and a depression on a surface, which is insulated from the first electrode over the substrate; a layer containing a light-emitting organic compound formed over the first electrode and the auxiliary electrode; and a second electrode formed over the layer containing the light-emitting organic compound. At least part of the auxiliary electrode is electrically connected to the second electrode
Implementation Method 2
The present invention relates to a solid-state light-emitting element utilizing electroluminescence (EL). By applying voltage to this element, light emission from the light-emitting organic compound can be obtained
Data Source
AI summary
Provided is a highly reliable light-emitting element in which damage to an EL layer is reduced even when an auxiliary electrode for an upper electrode is provided. Further, a highly reliable light-emitting device in which luminance unevenness is suppressed is provided. The light-emitting element includes a first electrode; an insulating layer over the first electrode; an auxiliary electrode having a projection and a depression on a surface, over the insulating layer; a layer containing a light-emitting organic compound over the first electrode and the auxiliary electrode; and a second electrode over the layer containing the light-emitting organic compound. At least part of the auxiliary electrode is electrically connected to the second electrode.